The present invention relates to a piezoelectric/electrostrictive ceramic composition, a piezoelectric/electrostrictive body, and a piezoelectric/electrostrictive film device. More particularly, the present invention relates to a piezoelectric/electrostrictive ceramic composition capable of constituting a piezoelectric/electrostrictive body or a piezoelectric/electrostrictive portion both having an excellent piezoelectric/electrostrictive property and durability even under high-temperature and highly humid conditions; a piezoelectric/electrostrictive body having an excellent piezoelectric/electrostrictive property and durability even under high-temperature and highly humid conditions; and a piezoelectric/electrostrictive film device comprising, a piezoelectric/electrostrictive portion having an excellent piezoelectric/electrostrictive property and durability even under high-temperature and highly humid conditions.
As an device capable of controlling a very fine displacement in a submicron order, piezoelectric/electrostrictive film devices have been known. In particular, a piezoelectric/electrostrictive device formed by laminating, on a substrate made of a ceramic, a piezoelectric/electrostrictive portion made of a piezoelectric/electrostrictive ceramic composition and electrode portions to which a voltage is applied, is suitable for control of a very fine displacement and moreover has superior properties such as high electromechanical transduction efficiency, high-speed response, high durability, low power consumption and the like. Therefore, the piezoelectric/electrostrictive device is in use in various applications such as piezoelectric pressure sensor, probe-transferring mechanism in scanning tunneling microscope, rectilinear guide mechanism in ultra-precision processing apparatus, servo valve for hydraulic system, head of VTR, picture device constituting flat panel type image display, head of ink jet printer, and the like.
Meanwhile, various investigations have been made on the piezoelectric/electrostrictive ceramic composition constituting the piezoelectric/electrostrictive portion of piezoelectric/electrostrictive film device. There is disclosed, for example, a Pb(Mg1/3Nb2/3)O3—PbTiO3—PbZrO3 ternary solid solution system composition, or a piezoelectric/electrostrictive ceramic composition wherein, in the above ternary composition, part of Pb is substituted with Sr, La or the like (reference is made to, for example, JP-B-44-17103 and JP-B-45-8145). Such a composition is expected to be able to constitute, in a piezoelectric/electrostrictive device, a piezoelectric/electrostrictive portion (which is the most important portion of the device and determines the piezoelectric property of the device) superior in piezoelectric property (e.g. piezoelectric d constant).
Conventional piezoelectric/electrostrictive devices have had a problem in that, when placed or used in severe conditions such as high-temperature (35° C. or higher) condition, highly humid (80% RH or higher) condition, and the like, they tend to show a reduction in flexural displacement. Further, when they are placed or used in such severe conditions and, for example, a high electric field is applied, they generate, in some cases, micro-cracks in the piezoelectric/electrostrictive portion. Therefore, particularly when they undergo repeated flexural displacement a large number of times, their durability tends to decrease rapidly and there has been a problem in that their initial piezoelectric/electrostrictive property can not be exhibited.
Piezoelectric/electrostrictive devices are considered to be placed in various environments and used repeatedly, depending upon the applications. For example, when used as a sensor, they may be placed in, for example, the outdoors where no air-conditioner or the like is installed. Hence, it is desired to develop a piezoelectric/electrostrictive body and a piezoelectric/electrostrictive device both having sufficient durability even when placed and used under relatively severe conditions.